Identify the oxidation state of the metal in each of the following compounds.

(a) Co(NH3)3(NO2)3

(b) [Ag(NH3)2]NO3

(c) K3[Cr(C2O4)2Cl2]

(d) Cs[CuCl2]

Video transcript

Welcome, everybody. Here's our next problem, determine the oxidation number of the central metal in each complex ion. And we have three different complex ions and four different answer choices A through D, each of which has three different possibilities for that charge. So we'll go into these in more detail as we work our way through the complexes. So number one has in brackets with an overall charge of three minus fe and then in parenthesis, CN subscript six. So we have a complex with an overall negative three charge with a central ion of iron and six cyanide ligands. So we need to think about the char oxidation state of our metal ion. So our overall charge is negative three. So right, negative three equals the oxidation state of iron. So os fe plus and now we need the oxidation state of our ligands, cyanide has a negative one charge. So we have negative one multiplied by six ligands. So if we rearrange this equation to solve for the oxidation state of iron, we have the oxidation set of iron equals negative three plus six. So that equals positive three. So if we look at answer choice, a it says for number one oxidation state of iron is positive three. So that's correct. In choice B for number one, it says oxidation state of iron is positive four. So that's incorrect. And we can rule out choice B for choice C, it says number one oxidation state of iron is positive three. So that's correct. And for choice D, number one, it says oxidation state of iron is positive too, that's incorrect. And we rule out choice D. So let's move on to our next complex. Number two, we have in brackets with an overall charge of two plus N I and then in parentheses, NH three. So we've got a complex with an overall charge of positive two, a nickel as our metal atom and we have an ammonia ligand. So the ammonia ligand is neutral. So that would be a charge of zero there. So our overall charge is positive two. So we say positive two equals the oxidation state of nickel plus zero. So that means the oxidation state of nickel must equal positive two minus zero. So positive two. So if we look at choice A for number two, it says the oxidation state of nickel is positive too. So that's correct. We've already already eliminated. Choice B for choice C number two, it says oxidation state of nickel is positive three. So that's incorrect. And we can rule out choice C and then choice D we've already ruled out. So we've actually now eliminated all but choice a so on a test in the interest of time, I would pick a and keep on going. But because we're doing a practice problem, we'll be thorough and look at number three. So number three, our overall charge we have in brackets, the overall charge being two plus we have ZN and then in parentheses, H2O subscript six. So we have an overall charge of positive two equals. Our complex has zinc as a metal ion and six water ligands, water has a neutral charge. So our positive two equals the oxidation state of zinc plus zero. So the oxidation state Z equals and it will be positive too minus zero. So it will be positive too. So we just double check that in choice. A number three says oxidation state of zinc is positive too. So we've worked through all of these. The oxidation number of the central metal in each complex ion is choice. A number one oxidation state of iron is plus three. Number two, oxidation state of nickel is plus two and number three oxidation state of zinc is plus two. See you in the next video.